bn_high.c

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#include <stdio.h>
#include "cryptlib.h"
#include "bn_lcl.h"

#undef BN_MUL_HIGH_DEBUG

#ifdef BN_MUL_HIGH_DEBUG
#define debug_BN_print(a,b,c) BN_print_fp(a,b); printf(c);
#else
#define debug_BN_print(a,b,c)
#endif

int BN_mul_high(BIGNUM *r,BIGNUM *a,BIGNUM *b,BIGNUM *low, int words);

#undef t1
#undef t2

int BN_mul_high(r,a,b,low,words)
BIGNUM *r,*a,*b,*low;
int words;
	{
	int w2,borrow=0,full=0;
	BIGNUM t1,t2,t3,h,ah,al,bh,bl,m,s0,s1;
	BN_ULONG ul1,ul2;
	
	BN_mul(r,a,b);
	BN_rshift(r,r,words*BN_BITS2);
	return(1);

	w2=(words+1)/2;

#ifdef BN_MUL_HIGH_DEBUG
fprintf(stdout,"words=%d w2=%d\n",words,w2);
#endif
debug_BN_print(stdout,a," a\n");
debug_BN_print(stdout,b," b\n");
debug_BN_print(stdout,low," low\n");
	BN_init(&al); BN_init(&ah);
	BN_init(&bl); BN_init(&bh);
	BN_init(&t1); BN_init(&t2); BN_init(&t3);
	BN_init(&s0); BN_init(&s1);
	BN_init(&h); BN_init(&m);

	bn_set_low (&al,a,w2);
	bn_set_high(&ah,a,w2);
	bn_set_low (&bl,b,w2);
	bn_set_high(&bh,b,w2);

	bn_set_low(&s0,low,w2);
	bn_set_high(&s1,low,w2);

debug_BN_print(stdout,&al," al\n");
debug_BN_print(stdout,&ah," ah\n");
debug_BN_print(stdout,&bl," bl\n");
debug_BN_print(stdout,&bh," bh\n");
debug_BN_print(stdout,&s0," s0\n");
debug_BN_print(stdout,&s1," s1\n");

	/* Calculate (al-ah)*(bh-bl) */
	BN_sub(&t1,&al,&ah);
	BN_sub(&t2,&bh,&bl);
	BN_mul(&m,&t1,&t2);

	/* Calculate ah*bh */
	BN_mul(&h,&ah,&bh);

	/* s0 == low(al*bl)
	 * s1 == low(ah*bh)+low((al-ah)*(bh-bl))+low(al*bl)+high(al*bl)
	 * We know s0 and s1 so the only unknown is high(al*bl)
	 * high(al*bl) == s1 - low(ah*bh+(al-ah)*(bh-bl)+s0)
	 */
	BN_add(&m,&m,&h);
	BN_add(&t2,&m,&s0);

debug_BN_print(stdout,&t2," middle value\n");

	/* Quick and dirty mask off of high words */
	if (w2 < t2.top) t2.top=w2;
#if 0
	bn_set_low(&t3,&t2,w2);
#endif

debug_BN_print(stdout,&t2," low middle value\n");
	BN_sub(&t1,&s1,&t2);

	if (t1.neg)
		{
debug_BN_print(stdout,&t1," before\n");
		BN_zero(&t2);
		BN_set_bit(&t2,w2*BN_BITS2);
		BN_add(&t1,&t2,&t1);
		/* BN_mask_bits(&t1,w2*BN_BITS2); */
		/* if (words < t1.top) t1.top=words; */
debug_BN_print(stdout,&t1," after\n");
		borrow=1;
		}

/* XXXXX SPEED THIS UP */
	/* al*bl == high(al*bl)<<words+s0 */
	BN_lshift(&t1,&t1,w2*BN_BITS2);
	BN_add(&t1,&t1,&s0);
	if (w2*2 < t1.top) t1.top=w2*2; /* This should not happen? */
	
	/* We now have
	 * al*bl			- t1
	 * (al-ah)*(bh-bl)+ah*bh	- m
	 * ah*bh			- h
	 */
#if 0
	BN_add(&m,&m,&t1);
debug_BN_print(stdout,&t1," s10\n");
debug_BN_print(stdout,&m," s21\n");
debug_BN_print(stdout,&h," s32\n");
	BN_lshift(&m,&m,w2*BN_BITS2);
	BN_lshift(&h,&h,w2*2*BN_BITS2);
	BN_add(r,&m,&t1);
	BN_add(r,r,&h);
	BN_rshift(r,r,w2*2*BN_BITS2);
#else
	BN_add(&m,&m,&t1); 		/* Do a cmp then +1 if needed? */
	bn_set_high(&t3,&t1,w2);
	BN_add(&m,&m,&t3);
	bn_set_high(&t3,&m,w2);
	BN_add(r,&h,&t3);
#endif

#ifdef BN_MUL_HIGH_DEBUG
printf("carry=%d\n",borrow);
#endif
debug_BN_print(stdout,r," ret\n");
	BN_free(&t1); BN_free(&t2);
	BN_free(&m); BN_free(&h);
	return(1);
	}